1. Field of Invention
The present invention relates to a method for producing a semiconductor device. The present invention aims to improve a conventional batch system, in which a plurality of semiconductor-silicon wafers are treated by chemical vapor deposition (CVD) or a direct reaction of the wafers with a reaction gas, so that the growth rate of the CVD films and the like is enhanced. The present invention also relates to an apparatus for producing a semiconductor device.
2. Description of Related Art
Long history is involved in the LP (low-pressure)-CVD methods using the hot-wall type heating furnace. A plurality of the semiconductor silicon wafers are located horizontally in the reaction tube which is installed in the furnace. The LP-CVD methods reported in the literature are related to the formation of SiO.sub.2 film for example with the use of TEOS and ozone, PSG (phosphosilicate glass) film, BPSG (borophospho-silicate glass) film, HTO (high-temperature oxidation) film with the use of SiH and N.sub.2 O or NO, Si.sub.3 N.sub.4 film, Ta.sub.2 O.sub.5 film, WSi.sub.2 film or the like.
In a conventional vertical hot-wall type heating furnace approximately 150 wafers can be treated in one batch. Although the treatment time is long in such a furnace, since the thermal stress can be mitigated, the above-mentioned furnace is advantageous for producing fine devices. Each wafer is or a plurality of wafers together are loaded into and unloaded from such a furnace by means of a fork-shaped wafer-loading and unloading jig.
In a vertical hot-wall type heating furnace from approximately 100 to 150 wafers are arranged with a clearance distance of 5-9 mm, and the arranged wafers are located in a temperature-equalizing zone, the length of which is from 700 to 900 mm. The internal pressure of such furnace is kept as low as possible, for example approximately 0.3 to 1.0 torr so as to attain uniform growth of the film on each wafer. The reaction gas is introduced into a furnace at a speed as high as approximately 3 to 7 m/second. The introduced reaction gas first flows along the peripheral edges of the wafers within a quartz reaction tube in a direction perpendicular to the surface of wafers. The reaction gas is then engulfed into a clearance between the wafer surfaces.
Under such low-pressure condition, the growth rate of films ranges from 20 to 100 angstroms/minute and is slow. The growth rate of a film in the LP-CVD is influenced by the pressure and also by the length of the temperature-equalizing region. The growth rate of a film varies greatly dependent upon the position of the wafers with increase in the length of the temperature-equalizing zone. This length and hence the treated number of the 6-inch wafers are limited to keep the variation of film thickness usually within a range of from 1 to 3%. Especially, the growth rate of an HTO film ranges from 15 to 20 angstroms/minute at 800.degree. C. under the pressure of from 0.3 to 1.0 torr. Variation of the HTO film-thickness is from 3 to 6.5% on an 8-inch wafer and from 2 to 5% on a 6-inch wafer.
In the case of forming a P-doped or non-doped polycrystalline Si film with the use of SiH.sub.4 under the LP-CVD conditions of: 5 to 7 mm of the wafer-distance; 625.degree. C. of temperature; 200 mL/minute of the SiH.sub.4 flow rate; 50 to 150 8-inch wafers; and 0.6 torr of pressure, the growth rate is from 50 to 80 angstroms/minute. This growth rate is considerably less than the growth rate of a polycrystalline Si by means of a conventional single-wafer process by means of the lamp heating, which is the so-called cold-wall process.
The total processing time of 150 wafers, including the temperature-elevating and lowering stages, ranges from approximately 120 to 600 minutes. The total processing time is greatly dependent upon the kind and thickness of the film to be formed. An example of the long total processing time, i.e., 600 minutes or more, is the formation of an approximately 1 .mu.m thick amorphous Si.
As is described above, since the growth rate of a CVD film or a direct-reaction film is slow in the hot-wall process, its productivity can be enhanced by increasing the number of wafers treated in one batch, for example to 150 wafers.